This invention relates to a synthetic vascular graft, and more particularly to a drug delivery blood-tight collagen-impregnated synthetic vascular graft which does not need to be pre-clotted and which acts as a reservoir for sustained release of a drug material after implant.
The replacement of segments of human blood vessels with synthetic vascular grafts is well accepted in the art. Synthetic vascular grafts have taken a wide variety of configurations and are formed of a wide variety of materials. Among the accepted and successful vascular graft implants are those which are formed from a biologically compatible material which retains an open lumen to permit blood to flow through the synthetic graft after implant. The grafts may be made from biologically compatible fibers, such as Dacron and Teflon, may be knitted or woven and may be of a mono-filiment yarn, multi-filiment yarn or staple yarn.
An important factor in the selection of a particular graft substrate is the porosity of the fabric wall of which the graft is formed. Porosity is significant because it controls the tendency to hemorrhage during and after implantation and controls the ingrowth of tissue into the wall of the graft. It is desirable that the vascular graft substrate be sufficiently blood-tight to prevent the loss of blood during implant, yet the structure must be sufficiently porous to permit ingrowth of fibroblast and smooth muscle cells in order to attach the graft to the host tissue. Synthetic vascular grafts of the type described in U.S. Pat. Nos. 3,805,301 and 4,047,252, assigned to the assignee of the subject application, are elongated flexible tubular bodies formed of a yarn such as Dacron. In the earlier patent, the graft is a warp knitted tube and in the latter issued patent it is a double-velour synthetic graft marketed under the trademark Microvel. These types of grafts have sufficiently porous structures to permit ingrowth of host tissue.
The general procedure for implantation includes the step of pre-clotting, wherein the graft is immersed in the blood of the patient an allowed to stand for a period of time sufficient for clotting to insue. After pre-clotting, hemorrhaging does not occur when the graft is implanted and growth of tissue is not impeded. Graft infection is a most serious complication and occurs in an average of two percent of prosthetic graft placements. It is associated with a high risk of limb loss and patient mortality is as high as 75% depending on the location of the graft. While infection usually becomes evident soon after surgery, the time may be extended which leads to more serious consequences.
An absorbable collagen reinforced graft is proposed in U.S. Pat. No. 3,272,204 wherein the collagen is obtained from the deep flexor tendon of cattle. Another reinforced vascular prosthesis is described in U.S. Pat. No. 3,479,670 which includes an open mesh cylindrical tube wrapped by an outer helical wrapping of fused polypropylene mono-filiment filled with collagen fibrils which are claimed to render the prosthesis impermeable to bacteria and fluids. The collagen fibrils utilized are the same as described in U.S. Pat. No. 3,272,204.
The synthetic vascular grafts suggested by the prior art are claimed to be suitable for many applications. However, it is desirable to provide a flexible vascular graft having zero porosity, one which is receptive to ingrowth of host tissue and serves as a reservoir for drug materials to be released slowly from the surface of the graft following implant.